Fuel composition

ABSTRACT

Fuel compositions having improved low-temperature flow properties comprise wax-containing residual or flashed distillate hydrocarbon fuel having incorporated therein a minor amount of a copolymer of (1) an olefinically unsaturated compound containing an unbranched saturated hydrocarbon chain with at least 14 carbon atoms and (2) a heterocyclic compound which contains an olefinically unsaturated double bond not attached directly to a hetero atom and of which the ring carbon atoms linked to a hetero atom do not carry monovalent hydrocarbon groups, the heterocyclic compound most preferably being 4-vinylpyridine.

United States Patent [191 Van De Kraats et al.

[451 Feb. 25, 1975 1 FUEL COMPOSITION [73] Assignee: Shell Oil Company, New York, N.Y.

[22] Filed: Dec. 26, 1972 [21] Appl. No.: 318,355

[30] Foreign Application Priority Data Dec. 27, 1971 Netherlands 7117866 [52] 11.8. C1. 44/62, 44/64 [51] Int. Cl C101 1/14 [58] Field of Search 44/62, 63

[56] References Cited UNlTED STATES PATENTS 2,888,340 5/1959 Winnick 44/62 3,462,249 8/1969 Tunkel 44/63 FOREIGN PATENTS OR APPLICATIONS 1,154,966 6/1969 Great Britain Primary Examiner-Daniel E. Wyman Assistant Examiner-Y. H. Smith Attorney, Agent, or FirmHenry C. Geller [57] ABSTRACT Fuel compositions having improved low-temperature flow properties comprise wax-containing residual or flashed distillate hydrocarbon fuel having incorporated therein a minor amount of a copolymer of (1) an olefinically unsaturated compound containing an unbranched saturated hydrocarbon chain with at least 14 carbon atoms and (2) a heterocyclic compound which contains an olefinically unsaturated double bond not attached directly to a hetero atom and of which the ring carbon atoms linked to a hetero atom do not carry monovalent hydrocarbon groups, the heterocyclic compound most preferably being 4- vinylpyridine.

2 Claims, No Drawings FUEL COMPOSITION Background of the Invention Depending on the base material chosen and the method of preparation applied, fuels may contain paraffin wax. This wax settles out if the fuel is cooled to below a certain temperature. Upon further cooling more wax settles out until the mixture of wax and oil no longer flows. The lowest temperature observed in a standard laboratory test at which the waxy mixture still flows is called the pour point. The pour point of a fuel is of practical importance because it is an indication of the temperature at which the fuel no longer flows. 'In the future, problems associated with the flow properties of petroleum products will play a more important part, particularly in those cases where increasingly large quantities of waxy crude oil, such as that of African origin, will have to be handled.

Fuels are generally classified as residual fuels or distillate fuels. Residual fuels contain a certain percentage of residual components. The quantity of residual components in the fuel may vary within wide limits and mostly amounts to from 20 to 80 percent by weight or more of the total fuel. The residual components may have been obtained, for instance, as residue in the distillation of crude petroleum either at atmospheric pressure (long residue) or at reduced pressure (short residue). They may also be residues obtained in thermal or catalytic cracking processes. The residuals mostly having too high a viscosity, they are frequently blended with distillate oils, such as gas oils.

On the basis of their boiling ranges, distillate fuels can be roughly classified as gasolines, kerosenes'and gas oils. A special grade of distillate fuels is that of the so-called flashed distillates, which are prepared as follows: A crude oil is distilled at atmospheric pressure to a bottom temperature of about 350C. The residue thus obtained (long residue) is subsequently flashed under substantially reduced pressure to obtain a flashed distillate and a residue (short residue). In the flash distillation, the pre-heated feed is passed continuously into a flash chamber where evaporation takes place under constant equilibrium conditions. Gaseous and liquid products are continuously discharged. In flashing, fractionation is of no importance. The temperature at which flashing is carried out is limited to avoid cracking and coke formation. These side reactions become important if the temperature rises too far above 400C. Owing to the temperature limitations, flashing is conducted under highly reduced pressure in order to obtain distillate from a given residue (long residue) in a high yield. As a result, the flashed distillates contain higher boiling and melting paraffins which normally only occur in residues. In general these paraffins have melting points above about 35C, their boiling points usually being above about 350C. On account of the presence of these higher paraffins, which as a rule do not occur in the usual distillate fuels such as gas oils, the flashed distillates show a close relationship to the residual fuels, in particular with respect to their behavior at lower temperatures.

Fuels containing paraffins of the above-mentioned type have a wide field of use and depending on the specific application particular demands are made on the fuel. These demands are laid down in a number of specified properties, the most important of which relate to the pour point and the viscosity. These waxy fuels are used, for instance, as fuel oil for heating purposes and as fuel for low-speed diesel engines. In these applications, the pour point of the fuel plays a very important part.

It is known to depress the pour point of fuels containing paraffins which at least partly consist of paraffins with a melting point higher than about 35C and a boiling point higher than about 350C, by adding to these fuels polymers of olefinically unsaturated compounds at least part of which contains an unbranched saturated hydrocarbon chain with at least 18 carbon atoms; see, for example, British Pat. No. l,l54,966.

The thermal casehistory of the fuel, the temperature at which the polymer is added and the rate of cooling have been found to affect the temperature at which the fuel no longer flows. In actual practice the latter temperature is of paramount importance and, consequently, a test procedure comprising thermal treatment, temperature at which the polymer is added and slow cooling has been designed which is a very near approach to what happens to a fuel in practice during storage, transport and pumping and in which, in particular, the cooling of the fuel is carried out far more slowly than is usual in the laboratory methods for the determination of the pour point. Some fuels containing the above-mentioned polymers and having a desirable pour point (determined in the usual manner) were found, during a treatment linked up with what happens to a fuel in practice, to solidify at a higher temperature than the height of the pour point would suggest. This concerns in particular residualfuels containing at least about eight percent by weight of paraffins with a melting point above about 35C and a boiling point above about 350C.

SUMMARY OF THE INVENTION It has been found that under practical conditions of slow cooling in the above-described fuels it is only very specific copolymers that are instrumental in preserving good flow properties of the fuel at low temperatures. According to the invention, into a waxy hydrocarbon fuel, selected from the group consisting of a residual fuel and a flashed distillate, in which the paraffin waxes consist at least partly of paraffin waxes with a melting point above about 35C and a boiling point above about 350C are incorporated a minor amount of one or more copolymers of (1) an olefinically unsaturated compound containing an unbranched saturated hydrocarbon chain with at least 14 carbon atoms and (2) a heterocyclic compound which contains an olefinically unsaturated double bond not attached directly to a hetero atom and whose hetero atom linked ring carbon atoms do not carry monovalent hydrocarbon groups, the heterocyclic compound most preferably being 4- vinylpyridine.

The invention offers the advantage of improving the low-temperature flow properties of hydrocarbon fuels containing paraffins with a melting point above about 35C and a boiling point above about 350C in a simple and economically justified way such that the products obtained are suitable for practical use.

The invention is particularly important for the improvement of low-temperature flow properties of fuels comprising, at least in part, of residualcomponents and/or components obtained in the flashing of crude oil residues.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Besides the paraffins with a melting point above about 35C and a boiling point above about 350C the fuels may contain other paraffms. Depending on the blending ratio and the nature of the component of which the fuel is composed the total paraffin .content may vary within wide limits. The invention is particularly advantageous for waxy hydrocarbon fuels containing at least 8 percent by weight of those paraffms whose melting point is above about 35C and whose boiling point is above about 350C.

By olefinically unsaturated compounds comprising an unbranched saturated hydrocarbon chain with at least l4 carbon atoms is meant compounds containing, at least one, both the group C C and the group CH (CH ),,CH with n B 12. For the sake of brevity the terms long hydrocarbon chains? and long hydrocarbon side chains will be used hereinafter, by which are meant unbranched saturated hydrocarbon chains and hydrocarbon side chains, respectively, with at least 14 carbonatoms.

In order to be suitable for use in the present composition, the copolymers should contain long hydrocarbon side chains with at leastl4 carbon atoms. For practical use preference is given to copolymers with long hydrocarbon side chains in which the number of carbon atoms is at most 30 and in particular from 18 to 26.

The copolymers which can suitably be incorporated into the fuel composition according to the present invention consist of a backbone comprising main chains built of carbon atoms which main chains carry long hydrocarbon side chains. These long hydrocarbon side chains may be attached either directly or indirectly to the main chains. In the former case there are no further atoms between the first carbon atom of the long carbon side chain and the carbon atom of the main chain to which the side chain is attached. The long hydrocarbon side chain can be linked indirectly to the main chain between the first carbon atom of the longhydroearbon side chain and the carbon atom of the main chain to which the side chain is attached by one or more other atoms or groups, such as carbon atoms, oxygen atoms, sulfur atoms, nitrogen atoms or phosphorus atoms, or aromatic groups, for instance phenyl groups. Preferred are polymes in which the long hydrocarbon side chains are attached to the main chain either directly, or indirectly, via one or more oxygen and/or carbon atoms.

Such copolymers can in principle be prepared in two different manners. In the first place, these copolymers can be prepared by copolymerization ofolefinically unsaturated compounds which consist, at least in part, of olefinically unsaturated compounds comprising a long hydrocarbon chain. The copolymers can also be prepared by copolymerization of olefinically unsaturated compounds in which long hydrocarbon chains do not occur, long hydrocarbon chains subsequently being introduced into the copolymer as side chains. The heterocyclic compound may also be incorporated into the copolymer by copolymerization of a heterocyclic compound which contains an olefinically unsaturated double bond not linked directly to a hetero atom and of which the ring carbon, atoms attached to the hetero atom do not carry monovalent hydrocarbon groups, or the desired heterocyclic ring may be introduced into copolymers into which such a heterocyclic compound has not been incorporated by subsequent reaction.

If the copolymers are prepared by direct copolymerization of a monomer with long hydrocarbon chains and a heterocyclic compound which contains an olefinically unsaturated bond not attached directly to a hetero atom and of which the ring carbon atoms linked to a hetero atom do not carry monovalent hydrocarbon groups, a very suitable starting material is a mixture of monomers comprising the two monomers mentioned. Radical copolymerization can suitably be used. if required one or both monomers are added during the polymerization so as to obtain a copolymer of a more homogeneous composition, i.e., a copolymer in which in all copolymer molecules the ratio of units originating from the said two types of monomer differs only slightly.-

Exernplary of olefinically unsaturated compounds in which long hydrocarbon chains occur and which can be used for the preparation of copolymers for use in the present fuel are: alkylstyrenes and acylstyrenes, such as p-octadecylstyrene, vinyl esters and allyl esters of saturated aliphatic monocarboxylic acids, such as vinyl esters and allyl esters of arachidic acid and behenic acid; alkyl esters of olefinically unsaturated lower aliphatic monocarboxylic acids, such as n-octadecyl acrylate and n-eicosyl methacrylate; alkyl amides of unsaturated aliphatic monocarboxylic acids, such as n-eicosyl acrylamide and n-docosyl methacrylamide; dialkyl esters of unsaturated aliphatic dicarboxylic acids, such as di-noctadecyl maleate and di-n-tetracosyl fumarate; dialkyl amides of unsaturated aliphatic dicarboxylic acids, such as di-n-eieosyl maleic acid diamide and di-ndocosyl fumaric acid diamide; imides of unsaturated aliphatic dicarboxylic acids, such as n-octadecyl maleic acid imide and n-eicosyl maleic acid imide; alkyl vinyl ethers such as n-docosyl vinyl ether and n-tetracosyl vinyl ether; and monoolefins, such as octacosene-l and docosene-l. Preferred are C to C alkyl esters of olefinically unsaturated C to C monocarboxylic acids, such as acrylic and methacrylic acid, and particularly preferred are the alkyl acrylates.

As used herein heterocyclic compounds means compounds which contain a heterocyclic ring. The expression olefinically unsaturated double bonds not attached direct to a hetero atom" means that no carbon atom which is linked to another carbon atom by an olefinically unsaturated double bond is linked direct to a hetero atom in the heterocyclic ring. By monovalent hydrocarbon groups is meant groups which consist exclusively of carbon and hydrogen, and which can be linked to another atom in only one phase.

Very suitable heterocyclic compounds which contain olefinically unsaturated double bonds not attached direct to a hetero atom and of which the ring carbon atoms linked to a hetero atom do not carry monovalent hydrocarbon groups are compounds containing one hetero atom in the ring. The hetero atoms in the heterocyclic ring can very suitably be sulfur, oxygen or phosphorus atoms, nitrogen atoms being preferred. Exemplary of heterocyclic compounds that can conveniently be used are sulfolene, 4-vinylpiperidine, heterocyclic compounds containing a pyridine ring being preferred. The olefinically unsaturated double bond present in the heterocyclic compound suitably occurs in a vinyl group. Most preferred as the heterocyclic compound of the copolymer of the present composition is 4- vinylpyridine.

If desired, olefinically unsaturated compounds which neither contain a long hydrocarbon chain nor are heterocyclic compounds with the above-mentioned characteristics may be present during the copolymerization and be incorporated into the copolymer. Exemplary of this type are vinyl esters and allyl esters of saturated monocarboxylic acids, such as vinyl esters and allyl esters of acetic acid; alkyl esters of unsaturated monocarboxylic acids, such as methyl methacrylate and isobutyl acrylate; dialkyl esters of unsaturated dicarboxylic acids, such as diethyl maleate and dioctyl fumarate; alkyl vinyl ethers, such as octyl vinyl ether and lauryl vinyl ether; and monoolefins, such as ethene and butene-l.

Depending on the nature of the paraffin waxes having a melting point above about 35C and a boiling point above about 350C present in the fuel, it may be preferable to incorporate one or more copolymers in which the long hydrocarbon side chains differ from one another in length by a number of carbon atoms.

The ratio of the number of units, incorporated into the copolymers, originating from an olefinically unsaturated compound which contains an unbranched saturated hydrocarbon chain with at least 14 carbon atoms to the number of units originating from a heterocyclic compound which contains an olefinically unsaturated double bond not attached directly to a hetero atom and of which the ring carbon atoms linked to a hetero atom do not carry monovalent hydrocarbon groups may vary within wide limits. A ratio between 1:5 and :1, that is, 02-1011, and particularly 2:1 and 511, that is 2-511, is very suitable.

The molecular weight of the copolymers of the present composition may vary within the wide limits. For practical application preferably copolymers are chosen which have a number average molecular weight between 1,000 and one million, and particularly between 3,000 and 100,000.

The concentration in which the polymers may be used may vary within wide limits, depending on the nature, the structure and the molecular weight of the polymer to be applied, the nature and quantity of the paraffin waxes present in the fuel, and the desired effect. In some cases a quantity as small as about 0.001 percent by weight calculated on the fuel composition may be sufficient for obtaining greatly improved lowtemperature flow properties. In most cases a quantity of about 2.0 percent by weight is amply sufficient. It is preferred to incorporate from about 0.01 to about 0.5 percent by weight of the polymers into the fuel.

The present fuel compositions can, in addition to the polymers of the invention improving the lowtemperature flow properties, also contain small quantities of other compounds which will generally be added to fuels of this type. Examples of such compounds are antioxidants, anti-corrosion additives, metal deactivators and additives preventing filter blockage and formation of emulsions.

EXAMPLES A copolymer accordingto the invention was prepared by copolymerization, at 71C, of a mixture of alkyl acrylates, which alkyl groups contained an average of 21 carbon atoms, and 4-vinylpridine in toluene in the presence of 0.08% azoisobutyronitrile as catalyst. At the start of the polymerization the molar ratio of alkyl acrylate to 4-vinylpyridine was 110.098; during the polymerization (6 hours) 4-viny1pyridine was gradually added. The polymerization was terminated when of the monomers originally present had been converted. In the copolymer obtained the ratio of the units originating from alkyl acrylate to those from 4- vinylpyridine was 3.611; the number average molecular weight of the copolymer was 45000 (polymer A).

In an analogous way, two copolymers not according to the invention was prepared starting from the alkyl acrylate described above and 2-vinylpyridine (polymer B) and 2-vinyl-5-ethylpyridine (polymer C), respectively. In these copolymers the ratio of the units originating from alkyl acrylate to those from the vinylpyridines was practically identical with that of polymer A, as also was the molecular weight. In the experiments to be described further was included for comparison a homopolymer of alkyl acrylates which contained alkyl groups with an average of 20 carbon atoms and which had a molecular weight of 55000 (polymer D).

Polymers A, B, C and D were dissolved in four types or residual fuel. Fuel 1 was based on a residue of an atmospheric distillation of a North African crude oil and had a kinematic viscosity at 50C of 134 cS; fuel 11 (kinematic viscosity at 50C, 21 cS) was based on a residue of an atmospheric distillation of a Venezuelan crude oil and contained 56.6%w distillate; fuel 11] was based on a residue of an atmospheric distillation of a Nigerian crude oil with a kinematic viscosity of 60 08 at 50C; and fuel 1V contained 83%w of fuel 111 and 1.7%w of gas oil and had a kinematic viscosity of 30 cS at 50C. Table 1 shows the contents of paraffins with a melting point above about 35C and a boiling point above about 350C.

The pour points of the fuels which did or did not contain polymers A, B, C or D were determined in the following way:

The fuel is heated to 104C with stirring, next poured into a test tube and cooled down to 20C. Subsequently the sample is heated to 46C without stirring and the polymer is added in a concentration of 50% in toluene, after which the sample is cooled. Starting at 44C the test tube is carefully tilted after every 3C drop in temperature. The temperature at which the tube can be held horizontal for 5 seconds without the waxy mass starting to flow is called the solid point. The lowest temperature read before the solid point is reached, in other words, the lowest temperature'at which the paraffinic mixture still flows, is called the pour point. The pour point is obtained by adding 3C to the solid point temperature. The results of this pour point determination are given in Table 1 below.

From Table 1 it is seen that with this manner of pour determination the fuels containing polymer A have in all cases at least an equally low pour point as the same fuels with the same amounts of the polymers B, C and D; the superiority upon slow cooling of the fuels containing polymer A is not evident yet.

The solid point of the fuels upon slow cooling, which is in better agreement with the temperature changes taking place under actual field conditions, was determined by means of the following heating and cooling program. The fuel without polymer was heated to 104C, next cooled in an oil both overnight to 22C and kept at this temperature for seven days. Subsequently the temperature was raised to 65C and at this temperature (doping temperature) in a number of cases the polymer was added as a 50% concentrate in toluene. After that the temperature was lowered at a rate of 3C per day until the solid point had been reached. In a number of cases the addition of polymer to the polymcr-frcc fucl during this cooling was effected at 46C in stead of at 65C. This is program X. A program Y was conducted by heating the fuel compositions cooled to C according to program X to 45C and by subsequently lowering the temperature again by 3C per day until the solid point had been reached. The solid points determined according to this method are recorded in Table 2 below.

400 C 20 20 30 30 400 D 21 21 Z8 25 ll 7 0 15 15 0 0 200 A 15 l5 ll ll 200 D 15 15 -8 -1i 111 16 0 36 36 37 37 400 A g 26 Z3 Z7 27 400 B 26 26 33 33 400 C 26 30 33 33 400 D Z9 Z9 34 34 'l\/ 14 0 32 32 34 34 400 A 15 15 l2 12 400 B 30 30 33 33 400 C 30 30 33 33 400 D 29 29 31 31 Table 2 clearly shows that incorporation into residual fuels of polymer A according to the invention results, upon slow cooling, in a further lowering of the solid point than incorporation of polymers B, C and D. This holds in particular for the paraffin-rich fuels 1, I11 and W.

What is claimed is:

l. A residual fuel having improved low temperature flow properties wherein at least about 8% by weight of said fuel consists of waxes having a melting point greater than about 35C and a boiling point greater than about 350C, said fuel having incorporated therein from about 0.01 to about 0.05% by weight of a copolymer of (1) a C to C alkyl ester of acrylic acid and (2) 4-vinylpyridine, the copolymer having a number average molecular weight between 3,000 and 100,000 and a molar ratio of units from (1) to units from (2) of 2-51.

2. The composition of claim 1 wherein the alkyl of 

1. A RESIDUAL FUEL HAVING IMPROVED LOW-TEMPERATURE PROPERTIES WHEREIN AT LEAST ABOUT 8% BY WEIFHT OF FUEL CONSISTS OF WAXES HAVING A MELTING POINT GREATER THAN ABOUT 35*C AND A BOILING POINT GREATER THAN ABOUT 350*C, SAID FUEL HAVING INCORPORATED THEREIN FROM ABOUT 0.01 TO ABOUT 0.05% BY WEIGHT OF A COPOLYMER OF (1) A C18 TO C26 ALKYL ESTER OF ACRYLIC ACID AND (2) 4-VINYLPYRIDINE, THE COPOLYMER HAVING A NUMBER AVERAGE MOLECULAR WEIGHT BETWEEN 3,000 AND 100,000 AND A MOLAR RATIO OF UNITS FROM (1) TO UNITS FROM (2) OF 2-5:1.
 2. The composition of claim 1 wherein the alkyl of (1) is an average of 21 carbons. 